1. Sound production of the giant Madagascar cockroach, Gromphadorhina portentosa, was examined by behavioral and acoustical methods in order to determine the functions of the hisses produced by this species.

2. Gromphadorhina is able to produce audible hisses from a pair of modified spiracles. Adult males hiss in three social contexts: during aggressive encounters, during courtship (when two types of hisses are discernable), and during copulation. Adults and nymphs of both sexes also hiss when disturbed (Figs 2 and 3).

3. There are reliable differences among hisses emitted in these social contexts which depend on several features: the shape of the amplitude envelope (Fig. 4), the relative loudness (Table 1), and the temporal characteristics both of single hisses and of hiss trains (Table 1 and Fig. 4).

5. Males which have been silenced by occlusion of the specialized spiracles carry on apparently normal courtship, but they are unsuccessful in copulating due to a lack of receptive behavior by the female (Fig. 8).

6. Playback of recorded courtship hisses during courtship of females by silenced males leads to receptive behavior by females, and to normal rates of copulation (Fig. 8).

7. Our evidence supports the hypothesis that G. portentosa has evolved a system of communication in which hisses serve as auditory social signals.